NOT APPLICABLE
NOT APPLICABLE
1. Field of the Invention
This invention relates to electrophotographic printing. More specifically, this invention relates to electrophotographic printers which include a transfusing member.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98 Prior Art
Electrophotographic marking is a well known and commonly used method of copying or printing original documents. Electrophotographic marking is typically performed by exposing a light image of an original document onto a substantially uniformly charged photoreceptor. In response to that light image, the photoreceptor discharges so as to create an 2 v electrostatic latent image, thereby forming a toner powder image. That toner powder image is then transferred from the photoreceptor, either directly, or after an intermediate transfer step, onto a marking substrate such as a sheet of paper. The transferred toner powder image is then fused to the marking substrate using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the creation of another image.
The foregoing generally describes a typical black and white electrophotographic marking machine. Electrophotographic marking can also produce color images by repeating the above process once for each color that makes the color image. For example, the charged photoconductive surface may be exposed to a light image which represents a first color, say cyan (C). The resultant electrostatic latent image can then be developed with cyan toner particles to produce a cyan image which is subsequently transferred to a marking substrate. The foregoing process can then be repeated for a second color, say magenta (M), then, a third color, say yellow (Y), and finally a fourth color, say black (B). Beneficially each color toner image is transferred to the marking substrate in super-imposed registration so as to produce the desired composite toner powder image on the marking substrate.
The color printing process described above superimposes the various color toner powder images directly onto a marking substrate. Another electrophotographic color printing process uses an intermediate transfer member or belt (ITB). In systems which use such an ITB, successive toner images are transferred in superimposed registration from the photoreceptor onto the ITB. Only after the composite toner image is formed on the ITB is that image transferred and fused onto the marking substrate, e.g., paper.
The most common developing materials are dry powder toners. Dry powder developers are typically comprised of not only toner particles but also of carrier granules. The toner particles triboelectrically adhere to the carrier granules until the toner particles are attracted onto the latent image. An alternative to dry powder developing materials are liquid developers. Liquid developers, also referred to a liquid inks, have a liquid carrier into which toner particles are dispersed. When developing with liquid developers both the toner particles and the liquid carrier are advanced into contact with the electrostatic latent image. The liquid carrier is then removed by blotting, evaporation, or by some other means, leaving the toner particles behind.
ITBs can also be used in the fusing process. ITBs which are used in fusing are referred to herein as transfusing members or belts (TB), and the combined processes of transferring and fusing is called transfusing. Transfusing is highly desirable since the size and cost of transfusing printing machines can be less than comparable printing machines which use a separate transfer station and fusing station. Other advantages such as improved image quality can also be obtained by transfusing. Members are usually pinched between one or more contact rollers and a backup roller such that a fusing pressure is created between the nip of the backup roller and the transfusing member and heat is applied to the toner image. The combination of heat and pressure causes the toner image to fuse onto the marking substrate.
During the transfuse process, velocity control, e.g. by servo systems, of the photoreceptor drum and ITB is important to achieve a high quality image, e.g., proper color registration, lack of smearing, etc. The interface between the photoreceptor drum and the ITB is a slip interface. Hence, the motion of the four photoreceptors (C,M,Y,B) and the ITB can be independently controlled by separate servo systems. However, since the transfuse belt is a very sticky belt, no slip in the transfer nip between the ITB and TB is possible. Due to variations in encoding and mechanical tolerances, two different velocity measurements will be produced. If two different servo systems are used, they will have conflicting requirements. This makes independent velocity control of ITB and transfuse belt impossible.
It is therefore desirable to have method and apparatus for controlling the velocity of two or more engaged members.
An apparatus comprises first and second members having engaged and disengaged modes; a first velocity controller for controlling the velocity of the first member when it is disengaged from the second member; a second velocity controller for controlling the velocity of the second member when it is disengaged from the first member; one of said controllers commonly controlling both of said members when they are engaged.
A process comprises controlling the velocity of a first member; independently controlling the velocity of a second member when said first and second members are mutually disengaged; and commonly controlling the velocity of said members when said members are engaged.
Xerographic apparatus comprises at least one photoreceptor module; an image transfer member engaging said module; a transfuse member engagable and disengagable with said image transfer member; an image transfer member servo controller controlling the velocity of said image member when said members are disengaged; a transfuse member servo controller controlling the velocity of said transfuse member when said members are disengaged, one of said controllers controlling both of said members when they are mutually engaged.